Die warpage control for thin die assembly

Abstract

Die warpage is controlled for the assembly of thin dies. In one example, a semiconductor die has a back side and a front side opposite the back side. The back side has a semiconductor substrate and the front side has components formed over the semiconductor substrate in front side layers. A backside layer is formed over the backside of the semiconductor die to resist warpage of the die when the die is heated and a plurality of contacts are formed on the front side of the die to attach to a substrate.

What is claimed is: 
     
       1. An apparatus comprising:
 a semiconductor die having a back side and a front side opposite the back side, the back side having a semiconductor substrate and the front side having components formed over the semiconductor substrate in front side layers that induce a warpage of the die in a particular direction when the die is heated; 
 a back side layer over the back side of the semiconductor die to resist warpage of the die in the particular direction when the die is heated, the back side layer having a stress of at least −800 MPa and causing the die to have a warpage opposite the particular direction at room temperature; 
 a plurality of contacts on the front side of the die to attach to a substrate; and 
 a package substrate soldered to the plurality of contacts. 
 
     
     
       2. The apparatus of  claim 1 , wherein the semiconductor substrate has a coefficient of thermal expansion that is different from the front side layers to induce the warpage when heated. 
     
     
       3. The apparatus of  claim 1 , wherein the components of the front side layers comprise microelectronic circuitry. 
     
     
       4. The apparatus of  claim 1 , wherein the semiconductor substrate and front side layers are cut from a silicon wafer. 
     
     
       5. The apparatus of  claim 1 , wherein the back side layer comprises a pre-stressed deposition bonding layer over the back side of the semiconductor substrate, the apparatus further comprising a metallic deposition layer over the bonding layer. 
     
     
       6. The apparatus of  claim 5 , wherein the bonding layer is bonded to the die substrate and wherein the back side metallic layer is bonded to the bonding layer. 
     
     
       7. The apparatus of  claim 6 , wherein the bonding layer is a silicon nitride. 
     
     
       8. The apparatus of  claim 6 , wherein the metallic layer is copper. 
     
     
       9. The apparatus of  claim 1 , wherein the back side layer is pre-stressed TiW. 
     
     
       10. The apparatus of  claim 1 , wherein the back side layer is a sputtered pre-stressed layer. 
     
     
       11. The apparatus of  claim 1 , wherein the back side layer is a pre-stressed silicon nitride film over the semiconductor substrate, the apparatus further comprising an additional back side layer over the silicon nitride film. 
     
     
       12. The apparatus of  claim 1 , wherein the semiconductor substrate is thinned. 
     
     
       13. The apparatus of  claim 1 , wherein the front side layers induce a warpage of less than 20 μm in the die when the die is heated to a reflow temperature of 220° C. due to the back side layer. 
     
     
       14. A semiconductor package comprising:
 a package substrate; 
 a semiconductor die attached to the package substrate, the die having a plurality of contacts on a front side to attach to the package substrate and a thinned semiconductor substrate on a back side of the die to carry the contacts, the front side being opposite the back side, the back side having a semiconductor substrate and the front side having components formed over the semiconductor substrate in front side layers that are connected to the contacts and that induce a warpage of the die in a articular direction when the die is heated; and 
 a back side layer over the back side of the semiconductor die to resist warpage of the die in the particular direction when the die is heated, the back side layer having a stress of at least −800 MPa and causing the die to have a warpage opposite the particular direction at room temperature. 
 
     
     
       15. The package of  claim 14 , wherein the back side layer is a metallic layer having a coefficient of thermal expansion greater than the coefficient of thermal expansion of the front side layers. 
     
     
       16. The package of  claim 14 , wherein the back side layer comprises a bonding layer, the package further comprising a metallic layer deposited over the bonding layer. 
     
     
       17. The package of  claim 16 , wherein the bonding layer is a silicon nitride. 
     
     
       18. The package of  claim 16 , wherein the metallic layer is copper. 
     
     
       19. The package of  claim 16 , wherein the back side layer is pre-stressed TiW. 
     
     
       20. The package of  claim 14 , wherein the back side layer is a sputtered pre-stressed layer.